1. Field of the Invention
The present invention relates to a scroll compressor generally utilizable in air conditioning equipment for industrial use and home use.
2. Description of Related Art
The motor-driven compressor now in use in refrigerating systems is available in two types; that in which reciprocating pistons are employed and that in which rotary pistons are employed. Both are generally employed in air conditioning systems for industrial and home use and the use thereof is increasing as they have their own advantages and satisfactory performances. Recently, a new version of compressor known as a scroll compressor has gained a wide application because of its low-noise and low-vibration features.
FIG. 5 is a vertical sectional view showing an example of a conventional scroll compressor. As shown therein, a closed container 1 accommodates, in an upper portion thereof, a compression mechanism 2 comprising a stationary scroll 2a and an orbiting scroll 2b which is to undergo circular translation with a variable circular orbiting radius; a thrust bearing 3 for supporting the orbiting scroll 2b; and a bearing member 4 for supporting the thrust bearing 3. The orbiting scroll 2b has a shaft 2c inserted into an eccentric bearing 6 received in a hole 5b, that is defined at an end 5a of a crankshaft 5, so that the crankshaft 5 can drive the orbiting scroll 2b in one direction. An electric motor 7 includes a rotor 7a mounted on the crankshaft 5 for rotation together therewith, and a stator 7b fixed to the closed container 1 by means of shrinkage fit. The rotor 7a and the stator 7b are disposed below the bearing member 4 within the closed container 1. The crankshaft 5 is supported by a main bearing 8 of the bearing member 4 and an auxiliary bearing 23 thereof.
An oil reservoir 10 for accommodating a quantity of lubricating oil 9 is defined at the bottom of the closed container 1. A gas-sucking pipe 11 is provided on a side of the closed container 1. A gas pressure on the suction side acts on a lower portion of the closed container 1 below a spacer 22, whereas a gas pressure on the compression side acts on an upper portion of the closed container 1 above the spacer 22. The bearing member 4 has an oil exhaust port 12 defined therein for exhausting the lubricating oil 9 which has lubricated and cooled the main bearing 8, the auxiliary bearing 23, the eccentric bearing 6, and the thrust bearing 3. The crankshaft 5 has a through-hole 13 defined therein for supplying the lubricating oil 9 to each bearing, namely, the main bearing 8, the auxiliary bearing 23, the eccentric bearing 6, and the thrust bearing 3.
An oil guide 14 is fixed to the lower end of the crankshaft 5 by means of interference fit or by shrinkage fit so as to suck up the lubricating oil 9 from the oil reservoir 10. The closed container 1 further comprises an exhaust chamber 15 defined therein above the stationary scroll 2a and an exhaust pipe 16 for discharging compressed gas to the outside of the closed container 1. The stationary scroll 2a and the bearing member 4 are fastened to each other by bolts with the spacer 22 sandwiched therebetween. The stationary scroll 2a is of one-piece construction having a frame for fixing the stationary scroll 2a to the bearing member 4, and a wrap element integrally formed with the frame. The orbiting scroll 2b also has a wrap element integrally formed therewith. Each of the wrap elements has a spiral or involute shape required to compress gas.
The spacer 22 has its outer periphery fixed to the closed container 1 by welding, thus partitioning the interior of the closed container 1 into a lower portion on which a gas pressure on the suction side acts and an upper portion on which a gas pressure on the compression side acts.
The closed container 1 further comprises a check valve 19 for preventing a reverse rotation of the orbiting scroll 2b when the scroll compressor is stopped; a check valve guide 24 for restricting an axial movement of the check valve 19; an Oldham ring 20 for preventing the orbiting scroll 2b from rotating about its own axis but allowing it to undergo circular translation with respect to the stationary scroll 2a; and a suction port 21, defined in the bearing member 4, for supplying the compression mechanism 2 with low-pressure gas.
The operation of the compression mechanism 2 having the above-described construction will now be described below. The low-pressure gas is returned into the closed container 1 from the gas-sucking pipe 11 and draw into the compression mechanism 2. The orbiting scroll 2b undergoes circular translation with respect to the stationary scroll 2a, thus allowing the compression mechanism 2 to compress the gas drawn thereinto. Consequently, the pressure of the gas rises and enters the exhaust chamber 15. Then, the gas is discharged to the outside of the closed container 1 from the exhaust pipe 16. Low-pressure gas is introduced into the closed container 1 again and circulated therein, thereby completing a single cycle of compression well known to those skilled in the art.
On the other hand, the lubricating oil 9 sucked up by the oil guide 14 moves upward through the through-hole 13 in the crankshaft 5 to lubricate and cool the auxiliary bearing 23, the eccentric bearing 6, the thrust bearing 3, and the main bearing 8. Thereafter, the lubricating oil 9 is exhausted from the oil exhaust port 12 to an upper portion of the stator 7b and, then, returns to the oil reservoir 10 via a cut-out portion 18 of the stator 7b, thereby completing a lubricating cycle.
In order to manufacture a scroll compressor that is highly reliable, highly efficient, and inexpensive, it is important not only to use light component parts, but also select configurations of the component parts appropriate to forces which would act thereon during the use of the scroll compressor. Also, in order to manufacture the scroll compressor having a high efficiency, it is important to configure the wrap elements with high precision. In this respect, the number of processes required to manufacture a desired involute configuration affects the cost of the scroll compressor. Thus, it is necessary to process the wrap elements having a highly precise involute configuration with a high efficiency. In processing the wrap elements, particularly the wrap element of the stationary scroll 2a, the material thereof has a great influence on the process efficiency and process precision of the scroll compressor. Thus, it can be safely said that whether or not a scroll compressor which is inexpensive and highly efficient can be manufactured depends on the selection of the material of the wrap element of the stationary scroll 2a. A material which can be readily processed into the wrap element is costly. Also, in applications where readily processable eutectic graphite cast iron is used for the wrap element, it is difficult to configure the raw material into a desired configuration and, hence, a quantity of raw material more than necessary is required. Thus, the manufacture of an inexpensive scroll compressor cannot be expected.
In the case of the conventional scroll compressor, the stationary scroll comprises the frame for fixing the stationary scroll to the bearing member and to the spacer; and the wrap element having an involute shape required to compress gas. It is to be noted that the frame and the wrap element are integrally formed with each other. Mostly, the stationary scroll is made of cast iron. Formation of the stationary scroll having a complicated configuration causes the cost of the scroll compressor to be high. The selection of an inexpensive casting method necessitates preparation of a thick material, which leads to the formation of a thick stationary scroll. Consequently, the manufacturing cost becomes high due to the weight increase of the stationary scroll, the rise of a material cost, and the increase in machining allowance.
In the case of the conventional scroll compressor, the bearing member supporting the orbiting scroll via the thrust bearing, the spacer, and the stationary scroll are fastened to each other by means of bolts. During the operation of the compressor, force is applied to the stationary scroll and the orbiting scroll in the direction in which both scrolls move away from each other, due to the influence of compressed gas. Consequently, the compressed gas leaks, lowering the efficiency of the scroll compressor. In order to prevent this, a tip seal is provided at the leading end of each scroll. As a result, the manufacturing cost rises owing to the rise of material cost caused by the increase of the number of parts or owing to the increase of portions to be processed and assembled. Thus, the conventional art is incapable of manufacturing an inexpensive scroll compressor.
In addition, the compressed gas having a high temperature and pressure is exhausted to the periphery of the stationary scroll. Thus, the stationary scroll conducts heat from the compressed high-temperature gas, thus heating low-temperature gas introduced into the closed container and gas being compressed by the compression mechanism. Consequently, the efficiency of the scroll compressor is lowered, resulting in a reduction in volumetric efficiency.
The compressed gas having a high pressure flows backward toward the compressed gas having a low pressure when the compressor is stopped. Therefore, a check valve is required to minimize the period of time in which the orbiting scroll and the crankshaft rotate in reverse. It is important to shorten the period of time in which the orbiting scroll and the crankshaft rotate in reverse, so that the scroll compressor is reliable. To this end, it is necessary to dispose the check valve close to the compression mechanism so as to reduce the volume of high-pressure gas flowing backward. In the conventional compressor, the check valve is disposed immediately above the exhaust port of the stationary scroll. Thus, the check valve guide is required to prevent the check valve from being dislocated.